The object of the proposed research is the determination of the synaptic mechanisms and functional interconnections used in the vertebrate retina to process visual information. Of particular interest are the mechanisms controlling visual sensitivity in the rat retina during light and dark adaptation; lateral spread of adaptative effects; sites of photochemical dark adaptation; receptor mechanisms in the ground squirrel; differences between rod and cone adaptive mechanisms; light induced changes in extracellular potassium, (K).; changes in (K). activity during light and dark adaptation. These objectives will be approached by recording ganglion cell discharges from optic tract fibers of the rat and ground squirrel with metal microelectrodes and recording intraretinal responses from frog, rat, and marine toad retinas with ordinary glass micropipettes and potassium-specific ion-exchanger microelectrodes.